1. Field of the Invention
The present invention pertains to the art of household appliances and, more specifically, to a method and apparatus for thermoforming a plastic appliance door from two plastic sheets.
2. Discussion of the Prior Art
It is commonly known to produce a plastic appliance door, and in particular, a refrigerator door by independently manufacturing the various components that combine to make the door and then, in a separate manufacturing step, assembling the various components. For example, as represented in FIG. 1 of this application, it is common to form an outer refrigerator door panel 5 from a single stamped sheet of metal which is folded in order to form sides 8 and inwardly turned flanges 10. The inner liner 13 associated with such a refrigerator door is often thermoformed on a male mold member. In general, such an inner liner 13 is made on the male mold member because of the high draw ratios that would be involved with the use of a female mold member. Once the outer refrigerator door panel 5 and the inner refrigerator door liner 13 are formed, inner liner 13 is secured to door panel 5 along flanges 10, along with an annular gasket 16, by means of a plurality of connecting strips 18 and screws 20. A separate handle 22 is then secured to outer refrigerator door panel 5 by means of screws 24. Outer refrigerator door panel 5 is also generally formed with upper and lower aligned holes 27 which are adapted to receive pivot bushings 29 for mounting the assembled refrigerator door to a refrigerator cabinet. For insulation purposes, it is also known to inject foam between refrigerator door panel 5 and inner liner 13 after complete assembly of the refrigerator door.
The manufacturing procedure associated with constructing such a refrigerator door formed from various, individually produced components which are later assembled together, is inefficient. Such a process is extremely time consuming and requires various manufacturing stages wherein the individual components are made and assembled. In addition, since the outer refrigerator door panel 5 is made of metal, its outer surface must be painted for aesthetic purposes. The need for these multiple manufacturing stages obviously increases the overall costs associated with manufacturing such a refrigerator door.
It has also been proposed to manufacture a hollow refrigerator door formed entirely from plastic. Such an arrangement is generally shown in FIGS. 2, 3a and 3b and disclosed in U.S. Pat. No. 5,306,082. According to this method of making a refrigerator door, the first step in the manufacturing process involves independently making the individual components which combine to form the inner door members. As shown in FIG. 2, these inner components generally constitute opposing side members 35, 37 and a plurality of shelf defining members 40-42. In general, these interior components are separately blow molded by arranging two parallel sheets of plastic between first and second mold members (see FIGS. 3a and 3b), closing the mold members so as to pinch the sheets about outer perimeters thereof and injecting air between the sheets so as to cause the sheets to expand against the mold members. Side members 35, 37 and shelf members 40-42 are formed with tabs 45 which are adapted to extend within slots 48 formed in an outer door panel 50 that is constituted by a hollow plastic slab which is also blow molded. In a final stage of the blow molding of the outer door panel 50, the tabs 45 provided on side members 35, 37 and shelf members 40-42 are positioned within slots 48 such that slots 48 form about tabs 45 in order to secure side members 35, 37 and shelf members 40-42 to outer door panel 50. An annular gasket 52 is then secured by means of connecting strips 55 and screws 57 to an outer annular flange portion 59 of door panel 50. In addition, a separate handle 62 is secured to door panel 50 by means of screws 64.
The refrigerator door construction arrangement as represented by FIGS. 2, 3a and 3b has several advantages over the construction arrangement represented in FIG. 1 and discussed above. First, the entire refrigerator door of the FIG. 2 arrangement is formed from plastic and therefore its desired shape can be readily varied. In addition, such a manufacturing operation does not require a subsequent painting stage for outer door panel 50. Furthermore, making the outer door panel 50 from plastic can provide some additional heat efficiency benefits since the metal door panel of the FIG. 1 arrangement will be a better conductor of heat into the refrigerator than the plastic door. Finally, the use of plastic presents the ability to integrally form the outer door panel with a handle as also proposed in the prior art and represented in FIG. 4.
However, these previously proposed all-plastic refrigerator door arrangements suffer from various drawbacks. For example, the various components which make up each of the refrigerator doors are still separately manufactured and subsequently assembled. As indicated above, this is considered inefficient as it adds to the manufacturing time and cost associated with making such doors. Furthermore, the known all-plastic refrigerator door arrangements are generally not aesthetically appealing since the interconnection between the various components are often noticeably visible and there will be a pinch line where the mold halves close. Finally, although forming an outer door panel of plastic with an integrally formed handle reduces manufacturing costs associated with the outer door panel and is rather aesthetically appealing, the prior proposed system as represented in FIG. 4 forms the handle, generally indicated in 68, by creating a recess in the front surface 71 of the outer door panel 74 which inherently reduces the energy efficiency of the refrigerator door as a whole due to its reduced thickness.
Therefore, there exists a need in the art for a plastic refrigerator door which can be produced in a minimum number of manufacturing stages so as to reduce the manufacturing costs associated with the refrigerator door. In addition, there exists a need in the art for a all-plastic refrigerator door and method of making the same wherein the energy efficiency associated with the refrigerator door is maintained or increased. Finally, there exists a need in the art for an aesthetically appealing plastic refrigerator door.